Fluid Levels Uncertainty

You can use this method for modeling fluid level uncertainties if the range of uncertainty for gas-oil contact (GOC) and free water level (FWL) do not overlap each other. The definition of fluid levels is not dependent on each other and the values for FWL are always sampled deeper than the GOC. Also, either one or both fluid levels can be uncertain and defined accordingly.

Uncertain fluid levels form using the 'GOC - No overlap' method    click to enlarge

Using the GOC - No overlap method

• Enter the Reference value for GOC and FWL on this dialog or on the Fluid Levels form.
• Use the uncertainty symbol to open the Uncertainty parameter dialog and provide the statistical distribution of uncertain fluid levels.
• The Min and Max values for both fluid levels are listed on uncertain fluid levels dialog and must not overlap each other. Click Apply to save changes and keep working on this dialog, or click OK to go back to the Fluid Levels form.

In this method, the fluid levels are defined independently and it is relevant for fluid levels with an overlapping values of uncertainty ranges. If the realization samples the FWL shallower than the GOC, the weighting factor adjusts the sampled values of fluid levels to create a valid realization. In such cases, the adjustment using the weighting factor results in realization without an oil rim. For example, a weighting factor of 1 for FWL results in sampled value of FWL being used in the realization, with gas and water phase only.

Uncertain fluid levels form using the 'GOC - Weighted average' method    click to enlarge

Using the GOC - Weighted average method

• Weighting factor Click on the scale pointer and drag it to adjust the values, or use the mouse scroll wheel.
• Reference value Enter the reference value for fluid levels on this dialog or on the Fluid Levels form.
• Use the uncertainty symbol to open the Uncertainty parameter dialog and provide the statistical distribution of uncertain fluid levels. Note that both fluid levels must be set uncertain for this method.
• The Min and Max values for both the fluid levels, extracted from the uncertainty distribution, are listed on uncertain fluid levels dialog. Click Apply to save changes and keep working on this dialog, or click OK to go back to the Fluid Levels form.

In this method, the uncertainty for GOC is defined in terms of FWL and the oil column length. The FWL and the oil column length are uncertain parameters and the GOC uncertainty is dependent on both the parameters. The resulting GOC is the difference between the sampled FWL and the sampled oil column length, but limited to the shallowest possible oil depth (SPO).

Uncertain fluid levels form using the 'Oil column length' method    click to enlarge

Using the Oil column length method

• Shallowest possible oil depth (SPO) Enter the lowest depth value where oil is seen. The calculated GOC cannot be lower than the SPO.
• Oil column length reference value Enter the reference value for the oil column length.
• FWL Reference value for free water level.
• Use the uncertainty symbol to open the Uncertainty parameter dialog and provide the statistical distribution for oil column length and free water level.
  Important  Both FWL and oil column length must be uncertain parameters when using this method.
• Implied GOC (read only) Calculated using the sampled values from oil column length and FWL. Based on the previous inputs, an old reference value is listed along with the new reference value. The Min and Max values are also shown for the implied GOC, extracted from the sampled values of oil column length and FWL.
• Click Apply to save changes and keep working on this dialog, or click OK to go back to the Fluid Levels form.

In this method, the uncertainty of the GOC is dependent on the sampled FWL value, and the oil column length defined in percentage. On the dialog, you must also provide the Maximum oil column length (Max OCL) and the Shallowest possible oil depth (SPO). The FWL and the OCL% are uncertain parameters that must be defined to generate values for the GOC uncertainty range.

For each realization, an ‘Oil Column Length 100%’ (OCL 100%) value is generated. The product of OCL 100% and the sampled OCL% value gives the length of the oil column. So the resulting GOC value is the difference between the sampled FWL and the length of oil column generated in the previous step. Refer to the steps below to understand the calculation of GOC from the sampled FWL and OCL% values.

Calculation method used to generate GOC for each realization

1. OCL 100% = Min[(Sampled FWL - SPO), Max OCL]
2. Oil column length = OCL 100% * Sampled OCL%
3. Calculated GOC = Sampled FWL - Oil column length

Uncertain fluid levels form using the 'Oil column %' method    click to enlarge

Using the Oil column % method

• Shallowest possible oil depth (SPO) Enter the lowest depth value where oil is seen. The calculated GOC cannot be lower than the SPO.
• Max oil column length (Max OCL) Enter the value for the maximum oil column length.
• Oil column % reference value Reference value in percentage that is used to calculate the oil column length. This value can be between 0 to 100%.
• FWL Reference value for free water level.
• Use the uncertainty symbol to open the Uncertainty parameter dialog and provide the statistical distribution for oil column % and free water level. Note that it is obligatory that both FWL and oil column length are uncertain parameters when using this method.
• Implied GOC (read only) Calculated using the sampled values from oil column % and FWL. Based on the previous inputs, an old reference value is listed along with the new reference value. The Min and Max values are also shown for the implied GOC, generated using the sampled values of oil column % and FWL as described above.
• Click Apply to save changes and keep working on this dialog, or click OK to go back to the Fluid Levels form.